Hybrid electric vehicle incorporating an integrated propulsion system

ABSTRACT

A hybrid electric vehicle drive system comprising a combustion engine, an electric motor and at least one nickel metal hydride battery module forming a power source for providing electric power to the electric motor, the at least one nickel metal battery module having a peak power density in relation to energy density as defined by:  
       P &gt;1,420−16 E    
     where P is the peak power density as measured in Watts/kilogram and E is the energy density as measured in Watt-hours/kilogram.

RELATED APPLICATION INFORMATION

[0001] The present invention is a continuation of U.S. patentapplication Ser. No. 10/016,203 filed on Dec. 10, 2001 which is acontinuation of U.S. patent application Ser. No. 08/979,340 filed onNov. 24, 1997 which is a continuation-in-part of U.S. patent applicationSer. Nos. 08/792,358 and 08/792,359, both filed Jan. 31, 1997.

FIELD OF THE INVENTION

[0002] The present invention relates generally to a hybrid electricvehicle incorporating an integrated propulsion system. Morespecifically, this integrated propulsion system comprises a combustionengine, an electric motor, high specific power, high energy densitynickel-metal hydride (NiMH) batteries, and preferably a regenerativebraking system. The NiMH batteries of the invention have negativeelectrodes with substrates of enhance current collecting capabilities,positive electrodes having enhance conductivity, and other improvementsto enhance the power delivery capability of the battery and permitmaximum operating efficiency during charge and discharge cycling whilemaintaining a combination of energy density and power density whichprovides enhanced performance beyond the capabilities of prior art NiMHbattery systems.

BACKGROUND OF THE INVENTION

[0003] Advanced automotive battery development for vehicle propulsionhas, in the past, been directed primarily at the requirement of fullyelectric propulsion systems for such vehicles. To this end, StanfordOvshinsky and his battery development teams at Energy ConversionDevices, Inc. and Ovonic Battery Company have made great advances innickel-metal hydride battery technology for such applications.

[0004] Initially effort focused on metal hydride alloys for forming thenegative electrodes of such batteries. As a result of their efforts,they were able to greatly increase the reversible hydrogen storagecharacteristics required for efficient and economical batteryapplications, and produce batteries capable of high density energystorage, efficient reversibility, high electrical efficiency, efficientbulk hydrogen storage without structural changes or poisoning, longcycle life, and repeated deep discharge. The improved characteristics ofthese highly disordered “Ovonic” alloys, as they are now called, resultsfrom tailoring the local chemical order and hence the local structuralorder by the incorporation of selected modifier elements into a hostmatrix.

[0005] Disordered metal hydride alloys have a substantially increaseddensity of catalytically active sites and storage sites compared tosingle or multi-phase compositionally homogeneous crystalline materials.These additional sites are responsible for improved efficiency ofelectrochemical charging/discharging and an increase in electricalenergy storage capacity. The nature and number of storage sites can evenbe designed independently of the catalytically active sites. Morespecifically, these alloys are tailored to allow bulk storage of thedissociated hydrogen atoms at bonding strengths within the range ofreversibility suitable for use in secondary battery applications.

[0006] Some extremely efficient electrochemical hydrogen storagematerials were formulated, based on the disordered materials describedabove. These are the Ti—V—Zr—Ni type active materials such as disclosedin U.S. Pat. No. 4,551,400 (“the '400 Patent”) to Sapru, Hong, Fetcenko,and Venkatesan, the disclosure of which is incorporated by reference.These materials reversibly form hydrides in order to store hydrogen. Allthe materials used in the '400 Patent utilize a generic Ti—V—Nicomposition, where at least Ti, V, and Ni are present and may bemodified with Cr, Zr, and Al. The materials of the '400 Patent aremultiphase materials, which may contain, but are not limited to, one ormore phases with C₁₄ and C₁₅ type crystal structures.

[0007] Other Ti—V—Zr—Ni alloys are also used for rechargeable hydrogenstorage negative electrodes. One such family of materials are thosedescribed in U.S. Pat. No. 4,728,586 (“the '586 Patent”) to Venkatesan,Reichman, and Fetcenko, the disclosure of which is incorporated byreference. The '586 Patent describes a specific sub-class of theseTi—V—Ni—Zr alloys comprising Ti, V, Zr, Ni, and a fifth component, Cr.The '586 Patent, mentions the possibility of additives and modifiersbeyond the Ti, V, Zr, Ni, and Cr components of the alloys, and generallydiscusses specific additives and modifiers, the amounts and interactionsof these modifiers, and the particular benefits that could be expectedfrom them.

[0008] In contrast to the Ovonic alloys described above, the olderalloys were generally considered “ordered” materials that had differentchemistry, microstructure, and electrochemical characteristics. Theperformance of the early ordered materials was poor, but in the early1980's, as the degree of modification increased (that is as the numberand amount of elemental modifiers increased), their performance began toimprove significantly. This is due as much to the disorder contributedby the modifiers as it is to their electrical and chemical properties.This evolution of alloys from a specific class of “ordered” materials tothe current multicomponent, multiphase “disordered” alloys is shown inthe following patents: (i) U.S. Pat. No. 3,874,928; (ii) U.S. Pat. No.4,214,043; (iii) U.S. Pat. No. 4,107,395; (iv) U.S. Pat. No. 4,107,405;(v) U.S. Pat. No. 4,112,199; (vi) U.S. Pat. No. 4,125,688 (vii) U.S.Pat. No. 4,214,043; (viii) U.S. Pat. No.4,216,274; (ix) U.S. Pat. No.4,487,817; (x) U.S. Pat. No. 4,605,603; (xii). U.S. Pat. No. 4,696,873;and (xiii) U.S. Pat. No. 4,699,856. (These references are discussedextensively in U.S. Pat. No. 5,096,667 and this discussion isspecifically incorporated by reference). Additional discussion iscontained in the following U.S. patents, the contents of which arespecifically incorporated by reference: U.S. Pat. Nos. 5,104,617;5,238,756; 5,277,999; 5,407,761; 5,536,591; 5,506,069; and 5,554,456.

[0009] Ovshinsky and his teams next turned their attention to thepositive electrode of the batteries. The positive electrodes today aretypically pasted nickel electrodes, which consist of nickel hydroxideparticles in contact with a conductive network or substrate, preferablyhaving a high surface area. There have been several variants of theseelectrodes including the so-called plastic-bonded nickel electrodeswhich utilize graphite as a microconductor and also including theso-called foam-metal electrodes which utilize high porosity nickel foamas a substrate loaded with spherical nickel hydroxide particles andcobalt conductivity enhancing additives. Pasted electrodes of thefoam-metal type have started to penetrate the consumer market due totheir low cost and higher energy density relative to sintered nickelelectrodes.

[0010] Conventionally, the nickel battery electrode reaction has beenconsidered to be a one electron process involving oxidation of divalentnickel hydroxide to trivalent nickel oxyhydroxide on charge andsubsequent discharge of trivalent nickel oxyhydroxide to divalent nickelhydroxide. However, quadrivalent nickel is also involved in the nickelhydroxide redox reaction, the utilization of which has never beeninvestigated.

[0011] In practice, electrode capacity beyond the one-electron transfertheoretical capacity is not usually observed. One reason for this isincomplete utilization of the active material due to electricalisolation of oxidized material. Because reduced nickel hydroxidematerial has high electrical resistance, the reduction of nickelhydroxide adjacent the current collector forms a less conductive surfacethat interferes with the subsequent reduction of oxidized activematerial that is farther away.

[0012] Ovonic Battery Company has developed positive electrode materialsthat have demonstrated reliable transfer of more than one electron pernickel atom. Such stable, disordered positive electrode materials aredescribed in U.S. Pat. Nos. 5,344,728; 5,348,822; 5,523,182; 5,569,563;and 5,567,599; the contents of which are specifically incorporated byreference.

[0013] As a result of this research into the negative and positiveelectrode active materials, the Ovonic Nickel Metal Hydride (NiMH)battery has reached an advanced stage of development for EVs. Ovonicelectric vehicle batteries are capable of propelling an electric vehicleto over 370 miles (due to a specific energy of about 90 Wh/Kg), longcycle life (over 1000 cycles at 80% DOD), abuse tolerance, and rapidrecharge capability (up to 60% in 15 minutes). Additionally, the Ovonicbattery has demonstrated higher power density when evaluated for use asan EV stored energy source.

[0014] As an alternative to true electric vehicles, hybrid-electricvehicles (HEVs) have gained popularity as having the technicalcapability to meet the goal of tripling auto fuel economy in the nextdecade. Hybrid electric vehicles utilize the combination of a combustionengine and an electric motor driven from a battery and have beenproposed in a variety of configurations.

[0015] Hybrid systems have been divided into two broad categories,namely series and parallel systems. In a typical series system, anelectric propulsion motor is used to drive the vehicle and the engine isused to recharge the battery. In the parallel system, both thecombustion engine and the electric motor are used to drive the vehicleand can operate in parallel for this purpose.

[0016] There are further variations within these two broad categories.For example, there are systems which employ a combination of the seriesand parallel systems. In the so-called “dual mode” system, thepropulsion mode can be selected, either by the operator or by a computersystem, as either an “all electric” or “all engine” mode of propulsion.In the “range extender” system, a primarily electric system is used forpropulsion and the engine is used for peak loads and/or for rechargingthe battery. In the “power assist” system, peak loads are handled by thebattery driven electric motor.

[0017] A further division is made between systems which are “chargedepleting” in the one case and “charge sustaining” in another case. Inthe charge depleting system, the battery charge is gradually depletedduring use of the system and the battery thus has to be rechargedperiodically from an external power source, such as by means ofconnection to public utility power. In the charge sustaining system, thebattery is recharged during use in the vehicle, through regenerativebraking and also by means of electric power supplied from a generatordriven by the engine so that the charge of the battery is maintainedduring operation.

[0018] There are many different types of systems that fall within thecategories of “charge depleting” and “charge sustaining” and there arethus a number of variations within the foregoing examples which havebeen simplified for purposes of a general explanation of the differenttypes. However, it is to be noted in general that systems which are ofthe “charge depleting” type typically require a battery which has ahigher charge capacity (and thus a higher specific energy) than thosewhich are of the “charge sustaining” type if a commercially acceptabledriving range (miles between recharge) is to be attained in operation.Further and more specific discussion of the various types of HEVsystems, including “series”, “parallel” and “dual mode” types, and ofthe present invention embodied in such systems will be presented below.

[0019] In the present application, the phrase “combustion engine” isused to refer to engines running off of any known fuel, be it hydrogenor hydrocarbon based such as gasoline, alcohol, or natural gas, in anycombination.

[0020] The use of hybrid drive systems offers critical advantages forboth fuel economy and ultra-low emissions. Combustion engines achievemaximum efficiency and minimal emissions when operated at or near thedesign point speed and load conditions. Small electric motors arecapable of providing very high peak torque and power. Thus, the abilityto use a small combustion engine operating at maximum efficiency coupledwith an electric motor operating at maximum efficiency offers anoutstanding combination for minimizing emissions, providing excellentfuel economy, and maximizing acceleration.

[0021] A key enabling requirement for HEV systems is an energy storagesystem capable of providing very high peak power combined with highenergy density while at the same time accepting high regenerativebraking currents at very high efficiency. In addition, the duty cycle ofa peak power application requires exceptional cycle life at low depthsof discharge, particularly in charge depleting systems.

[0022] It is important to understand the different requirements for thisenergy storage system compared to those for a pure electric vehicle.Range is the critical factor for a practical EV, making energy densitythe critical evaluation parameter. Power and cycle life are certainlyimportant, but they are secondary to energy density for an EV. Alightweight, compact, high-capacity battery is the target for pure EVapplications.

[0023] In contrast, in HEV applications, gravimetric and volumetricpower density is the overwhelming consideration. Excellent cycle lifefrom 30 to 60% DOD is also more critical than cycle life at 80% DOD asrequired in EV applications. Similarly, rapid recharge is also essentialto allow efficient regenerative braking, and charge/discharge efficiencyis critical to maintain battery state of charge in the absence ofexternal charging. In addition, thermal management and excellent gasrecombination are important secondary considerations to rapid rechargingand multiple cycling.

[0024] Heat generated during charging and discharging NiMH batteries isnormally not a problem in small consumer batteries or even in largerbatteries when they are used singly for a limited period of time. On theother hand, batteries used in HEVs will be subjected to many rapidcharge and discharge cycles during normal operation. Such rapid chargingand discharging will result in significant thermal swings that canaffect the battery performance. The prior art suggests a variety ofsolutions to this problem, such as the following:

[0025] U.S. Pat. No. 4,115,630 to Van Ommering, et al., describes ametal oxide-hydrogen battery having bipolar electrodes arranged in acentrally drilled stack. This patent describes conducting heat generatedin the electrode stack via the hydrogen gas of the cell. In particular,the application notes that because heat conduction perpendicular toelectrode plates is 10-20 times smaller than conduction parallel toelectrode plates, cells using flat electrodes must be modifiedsignificantly which makes them unacceptably heavy.

[0026] J. Lee, et al. describe resistive heating and entropy heating inlead-acid and nickel/iron battery modules in 133(7) JESOAN 1286 (July,1986). This article states that the temperature of these batteries isdue to resistive heating and entropy changes of the electrochemicalreactions often varies considerably during their operation. They notethat the thermal resistance caused by the cell case plays an importantrole as the cell temperature becomes higher. This reference suggeststhat some additional cooling structure must be added to the battery.

[0027] U.S. Pat. No. 4,865,928 to Richter describes a method of removingheat from the interior of a high-performance lead acid battery byattaching a U-shaped tube to the negative electrode grid and circulatinga coolant through the tube.

[0028] U.S. Pat. No. 5,035,964 to Levinson, et al., describe attaching afinned heat sink to a battery and positioned the combination in achimney structure. The finned heat sink produces a convective flow ofair in the chimney to cool the battery and extend its life.

[0029] All of the above cited references suggest methods of removingheat that requires the addition of auxiliary apparatus to the batterypack. None suggest how this can be accomplished without modificationsthat, as U.S. Pat. No. 4,115,630 specifically states, result in anunacceptable addition to the total weight of the cell.

[0030] In all sealed cells, the discharge capacity of a nickel basedpositive electrode is limited by the amount of electrolyte, the amountof active material, and charging efficiency. The charge capacity of aNiMH negative electrode is limited by the amount of active materialused, since its charge efficiency is very high, nearly a full state ofcharge is reached. To maintain the optimum capacity for a metal hydrideelectrode, precautions must be taken to avoid oxygen recombination orhydrogen evolution before full charge is reached. This becomes acritical problem for batteries in any HEV system that undergo repetitivecharge and discharge cycles. The problem of venting is not new and manymanufacturers have attempted to solve it. Typically the solution hasinvolved the use of a gas consumption electrode (CCE). Typical GCEs arecarbon, copper, silver, or platinum prepared in a porous form to providea large surface area for gas recombination is the site of catalyticoxygen reduction.

[0031] U.S. Pat. No. 5,122,426 describes a GCE that has three distinctlayers, a hydrophobic electrically non-conductive first layer, ahydrophilic second layer, and a hydrophobic third layer. This thirdlayer is electrically connected to the negative electrode.

[0032] Similarly, U.S. Pat. No. 5,128,219 describes a gas consumptionelectrode comprising a metallic component, such as Pd, Ni, or Cu, and afilm of activated carbon, carbon black, and a binder. Use of thedescribed GCE is particularly discussed in a button cell.

[0033] While many GCEs are very efficient, their presence decreases thearea available for active electrodes and hence decreases the overallvolumetric energy density of the cell. In cells of an HEV system likeall sealed NiMH cells, it is desirable to keep pressures withinacceptable limitations without the necessity of using a GCE.

[0034] The foregoing are just a few examples of the differences inbattery requirements for EV applications and HEV applications. There arealso many other differences depending upon the particular type of HEVsystem employed. These will be discussed later in connection withparticular HEV systems. Given the fundamental differences inrequirements between the EV and those for an HEV application, it couldbe expected that those batteries currently optimized for use in EVapplications will generally not be suitable for HEV without increasingpower density. While the demonstrated performance of Ovonic EV batterieshas been impressive, these cell and battery designs have been optimizedfor use in pure EVs and therefore do not meet the specific requirementsfor HEVs.

SUMMARY OF THE INVENTION

[0035] An object of the present invention is a power system for a hybridvehicle comprising NiMH batteries having high peak power combined withhigh energy density and excellent cycle life at low depths of discharge.In particular, the present invention provides high peak power incombination with high energy density, a combination which the prior arthas been unable to provide, as will be explained.

[0036] Another object of the present invention is a power system for ahybrid vehicle comprising Ovonic NiNM batteries having high powercombined with high energy density, excellent low depth of dischargecycle life, good thermal management, and excellent gas recombination.

[0037] These and other aspects of the present invention are satisfied bya hybrid electric vehicle drive system comprising a combustion engine,an electric motor and at least one nickel metal hydride battery modulefor powering the electric motor, the at least one nickel metal batterymodule having a peak power density in relation to energy density asdefined by the following expression:

P>1,420−16E

[0038] where P is the peak power density as measured in Watts/kilogramand E is the energy density as measured in Watt-hours/kilogram.

[0039] Other aspects of the present invention are satisfied by a hybridelectric vehicle incorporating an integrated propulsion system,comprising: a power system comprising a combustion engine and anelectric motor, nickel metal hydride batteries configured for maximumpower and coupled to the power system, and power controlling meansgoverning the series and/or parallel operation of the combustion engineand the electric motor at maximum efficiency for powering the hybridelectric vehicle and providing for the charge and discharge of thenickel metal hydride batteries. Additionally, a regenerative brakingsystem may be coupled to the power controlling means and to provideadditional charging current for the nickel metal hydride batteries.

[0040] Other aspects of the battery are satisfied by the integratedpropulsion system described above, where the nickel-metal hydridebatteries have negative and/or positive electrodes comprising: powderedactive materials pressed into a porous metal substrate selected from thegroup consisting of copper, copper alloy, nickel coated with copper, andnickel coated with copper alloy. Additionally, the substrate may beplated with material that is electrically conductive and corrosionresistant.

[0041] Other aspects of the battery are satisfied by the integratedpropulsion system described above, where the porous metal substrate isfabricated with current collection lines having electrical conductivitygreater than the porous metal substrate, the current collection linesproviding high conductivity pathways from points remote from the currentcollecting tab on the negative and positive electrodes. To furtherincrease the conductivity between the components of the battery of theinvention and increase power, the current collecting tab may be laserwelded to themselves as well as to the terminals.

[0042] Other aspects of the battery are satisfied by the integratedpropulsion system described above, where the nickel metal hydridebatteries are low pressure nickel metal hydride electrochemical cells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043]FIG. 1 is a graphical depiction of the relationship between peakpower output and energy density of typical prior art nickel metalhydride batteries in comparison to the performance of the Ovonic nickelmetal hydride batteries of the present invention for various HEVapplications.

[0044]FIG. 2 is a schematic representation of a series BEV system inwhich the present invention can be embodied; specifically illustrated isthe matrix placement of the battery modules into the pack case, themanner in which the module spacers form coolant flow channels, fluidinlet and outlet ports, and fluid transport means.

[0045]FIG. 3 is a schematic representation of a parallel HEV system inwhich the present invention can be embodied.

[0046]FIG. 4 is a planar illustration of an electrode for a prismaticNi-MH battery with an attached electrode tab.

[0047]FIG. 5 is a stylized depiction of a top view of one embodiment ofthe fluid-cooled nickel metal hydride battery pack adopted for HEV usesof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0048] Nickel-metal hydride batteries of the present invention areadapted to provide increased specific power and recharge rates that areparticularly advantageous in HEV applications. These characteristics areprovided while maintaining a high energy density. This is accomplishedin the present invention through, inter alia, the use of positive andnegative electrodes having increased internal conductance. Suchelectrodes are formed by pressing powdered metal-hydride activematerials into highly conductive porous metal substrates. These porousmetal substrates are formed from copper, a copper alloy, or nickelcoated with copper or a copper alloy. Additionally, the substrate may beplated with a material that is electrically conductive and will preventcorrosion of the metal substrate in the battery environment, such asnickel.

[0049] With reference to FIG. 1, prior art NiMH batteries designed foruse in HEV applications have shown a maximum attainable energy densityof about 75 Wh/Kg while providing a peak power density capability ofabout 250 W/Kg. This combination of energy density and peak powerdensity is shown at point A in FIG. 1. Allowing for some minorengineering improvements, the peak power density attainable with priorart NiMH batteries at this energy density might be increased to about300 W/Kg with an energy density of about 70 Wh/Kg, which is shown atpoint B in FIG. 1. In order to increase the peak power density of suchprior art batteries for use in HEV systems, it is necessary to sacrificeenergy density as a trade off in order to attain a higher peak powerdensity. This, in turn, decreases the energy density of the battery sothat, for example, as the peak power density is increased from. 250 W/Kgto about 650 W/Kg for better HEV performance, the energy density isdecreased from about 70 Wh/Kg to about 45 Wh/Kg, as shown at point C inFIG. 1. Again, allowing for some engineering improvement, the peak powerdensity attainable at 45 Wh/Kg might be increased to about 700 W/Kg,which is point D in FIG. 1.

[0050] These points A, B, C and D define a band E which represents theupper limit of the region P (which region defines combinations of bothhigh power density and high energy density) attainable with prior artNiMH batteries for use in HEV systems. The present invention providesimproved performance in the region N yielding a unique combination ofboth higher energy density and higher energy density than has beenpossible to attain in battery modules adapted for use in HEVapplications.

[0051] Taking the upper limits of the shaded band E of FIG. 1, the upperlimit of peak power P density attainable for a selected given energydensity E of prior art NiMH battery modules for use in HEV applicationscan therefore be represented by the following equation:

P=1420−16E   Equation (1)

[0052] where P is the maximum available peak power density (measured inW/Kg) attainable for a given energy density E (measured in Wh/Kg). Thepresent invention permits operation of HEV systems of all types at peakpower density levels in relation to energy density in the region thatlies beyond this limits of the existing prior art, that is at levelshigher than those defined by the above equation (1).

[0053] For example, a battery module embodying the present invention andhaving an energy density of about 70 Wh/Kg typically exhibits a peakpower density of at least 600 W/Kg (shown at point F in FIG. 1) and canhave a peak power density as high as 1,000 W/Kg (shown at point G inFIG. 1). These points establish a band of peak power to energy densityrelationships particularly suited to BEV applications and which aresubstantially beyond the capability of prior art NiMH batteries.

[0054] To give specific examples, an Ovonic 60 Ah HEV battery embodyingthe present invention and having an energy density of about 70 Wh/Kgprovides a peak power of about 600 W/Kg. This is the example shown atpoint F in FIG. 1. In another example, an Ovonic 30 Ah HEV batteryembodying the invention and having an energy density of about 55 Wh/Kgprovides a peak power of about 550 W/Kg. This example is shown at pointG in FIG. 1. In a third example, an Ovonic 20 Ah HEV battery embodyingthe invention and having an energy density of about 50 Wh/Kg provides apeak power of about 600 W/Kg. This example is shown at point H in FIG.1.

[0055] Representative HEV systems in which the present invention isapplicable are shown in schematic form in FIGS. 2 and 3. FIG. 2 shows aseries HEV system in which a combustion engine 70 is connected to drivea generator 71. The generator 71 is in turn connected to charge abattery 72 which supplies electrical power to a drive motor 73. Thedrive motor 73 is connected to the vehicle drive system 74 whichsupplies drive power to the vehicle wheels.

[0056] The battery may be initially charged from a separate power sourcesuch as through an outlet connected to a public utility system. Thebattery 72 is also recharged to some extent by regenerative brakingduring deceleration.

[0057] In the parallel type of system as shown in FIG. 3, a battery 75is connected to supply electrical power to an electric drive motor 76which is connectible through a clutch 77 to vehicle drive system 78.Connected in parallel with the electric drive path formed by the battery75, the motor 76 and the clutch 77 is a combustion engine 79 which isalso connectible to the vehicle drive system 78. The vehicle can drivenby either the electric motor 76 when the clutch 77 alone is engaged orby the engine 79 when the clutch 80 alone is engaged, or by both themotor 76 and the engine 79 simultaneously when both clutches 77 and 80are engaged at the same time.

[0058] In the parallel system as shown in FIG. 3, the combustion engine79 may be sized much smaller than would otherwise be required to provideacceptable vehicle acceleration characteristics because the electricmotor 76 can be engaged along with the engine 79 to provide the desiredacceleration. This means that, if the combustion engine is used for theprimary drive mode, it can be operated at a much improved efficiencyunder steady state load and speed conditions.

[0059] Various combinations of the electric motor 76 and the combustionengine 79 are employed in parallel type systems. For example, in onesystem intended for use in city environments, vehicle propulsion isprovided by the electric motor 76 alone when the vehicle is operatedwithin the city. Outside of the city, the combustion engine 79 may beused for propulsion purposes. Various other combinations are alsoemployed using the parallel type of connection as shown in FIG. 3.

[0060] Parallel type systems such as shown in FIG. 3 are also operatedin either the charge sustaining or charge depleting mode as explainedabove. As shown in the diagram of FIG. 3, generative power feedbackduring regenerative braking. Other connections (not shown) can also beprovided to permit the combustion engine 79 to provide recharging powerto the battery 75 to implement a charge sustaining mode of operation.

[0061] For example, in the so-called “series-parallel” or “compound” HEVsystem, sometimes referred to as a “dual mode” system, a power splitteris used to take off some of the power from the combustion engine todrive a generator which provides recharging power to the battery.

[0062]FIG. 1 has been divided into sectors depicting those regions inwhich the various forms of HEV systems would be operated. In the regionPD, for example, systems which are of the charge depleting type wouldtypically be operated. This is because the battery is not rechargedduring operation and the emphasis will thus be on a high energy densityfor maximum range. This region is also referred to as the “rangeextender” region.

[0063] For the case of charge sustaining systems, where the battery isrecharged during operation, a lower energy density is accepted and theemphasis is on a higher peak power for improved performance with a lowerenergy density being accepted as a trade off for increase in powerdensity. This region is designated PS in the diagram of FIG. 1. Thisregion is also referred to as the “power assist” region.

[0064] Compound or dual mode systems would be operated in the region DSin between the regions CD and CS as shown in FIG. 1.

[0065] The parameter of peak power is determined in accordance withstandards established by the United States Advanced Battery Consortium(USABC). According to these standards, peak power is measured with thebattery module discharged to 50% depth of discharge. At this condition acurrent and corresponding power output which reduces the voltage of thebattery to ⅔ of its open circuit voltage held for a period of tenseconds is the peak power rating of the battery. This determination ismade under normal temperature conditions in the range of about 30 to 35°C.

[0066] The energy density or specific energy E is measured for thebattery module as designed for use in HEV applications. Thisdetermination is also made under normal temperature conditions in therange of about 30 to 35° C.

[0067] A battery module is an integral assembly of cells connectedtogether and encased in a casing and having external electricalconnections for connection to an external circuit or load.

[0068] As noted above, the present invention enables operation in thehigher performance region above the band E for all HEV system types,i.e., charge depleting, charge sustaining and dual operation. Prior artNiMH battery systems for HEV applications are unable to provideperformance in this enhanced performance region.

[0069] The power controlling means of the present invention that governsoperation of the combustion engine and the electric motor at maximumefficiency of said nickel metal hydride batteries can be any knowncontrol device. Preferably, the power controlling means is a solid stateintegrated microelectronic device including AI algorithms thatincorporate appropriate sensors and self-regulating and self-adjustingsub-routines. These permit constant adjustment of control parameters toattain maximum efficiency based on numerous external factors such astype of driving, average driving speed, ambient temperature, etc., aswell as system factors such as engine temperatures, charge/dischargetimes and rates, battery temperatures, fuel consumption, etc.

[0070] The electrodes can also include current collection lines on thesubstrate. Such current, collection lines have a higher electricalconductivity than the remainder of the substrate. This configurationassures high conductivity pathways from points remote from the currentcollecting tab on the electrode to the current collection tab. Oneembodiment of the current collection line comprises densifying portionsof the porous metal substrate. Another embodiment comprises wires,ribbons or sintered powder electrically attached or embedded into theporous metal substrate. These attached or embedded components can beformed from nickel, copper, a copper alloy, nickel coated with copper ora copper alloy, or a copper material coated nickel.

[0071] A primary consideration of the present invention involvesimproving the power output of an Ovonic nickel-metal hydride (NiMH)rechargeable battery. (While reference is made specifically to OvonicNiMH batteries, the principles described herein are applicable to alltypes of metal hydride battery systems regardless of their designation.)Generally, power output may be increased by lowering the internalresistance of the battery. Lowering the internal resistance decreasesthe power wasted due to heat dissipation within the battery, therebyincreasing the power which is available to drive external loads. Theinternal resistance of a nickel-metal hydride battery can be decreasedby increasing the conductivity of the battery components as well as theconnections between the components. More specifically, the internalresistance can be decreased by increasing the conductivity of both thepositive and negative electrodes of the battery.

[0072] The volumetric peak power density of the batteries of the presentinvention is generally ≧1500 W/L, preferably ≧1800 W/L, and mostpreferably ≧2700 W/L. The specific peak power density of batteries ofthe present invention is generally >600 W/kg, preferably ≧700 W/kg, andmost preferably ≧1000 W/kg. In batteries of the present invention, it isusually necessary to sacrifice energy density in favor of power density.With this in mind, the volumetric peak energy density of the batteriesof the present invention is generally between 130-250 Wh/L, preferably≧150 Wh/L, and most preferably ≧160 Wh/L.

[0073] In general, NiMH batteries employ a negative electrode having anactive material that is capable of reversible electrochemical storage ofhydrogen. Upon application of an electrical potential across a NiMHbattery, the active negative electrode material is charged by theelectrochemical absorption of hydrogen and the electrochemicalgeneration of hydroxyl ions. The electrochemical reaction at thenegative electrode is as follows:

[0074] The negative electrode reactions are reversible. Upon discharge,the stored hydrogen is released to form a water molecule and release anelectron.

[0075] The negative electrodes of a nickel-metal hydride battery aregenerally formed by pressing powdered active material into a porousmetal substrate. As discussed, the powdered active material of thenegative electrode is a hydrogen storage material. The hydrogen storagematerial may be chosen from the Ti—V—Zr—Ni active materials such asthose disclosed in U.S. Pat. No. 4,551,400 (“the '400 Patent”), thedisclosure of which is incorporated by reference. As discussed above,the materials used in the '400 Patent utilize a generic Ti—V—Nicomposition, where at least Ti, V, and Ni are present with at least oneor more of Cr, Zr, and Al. The materials of the '400 Patent aremultiphase materials, which may contain, but are not limited to, one ormore phases with C₁₄ and C₁₅ type crystal structures.

[0076] There are other Ti—V—Zr—Ni alloys which may also be used for thehydrogen storage material of the negative electrode. One family ofmaterials are those described in U.S. Pat. No. 4,728,586 (“the '586Patent”), the disclosure of which is incorporated by reference. The '586Patent discloses a specific sub-class of these Ti—V—Ni—Zr alloyscomprising T, V, Zr, Ni, and a fifth component, Cr. The '586 Patentmentions the possibility of additives and modifiers beyond the T, V, Zr,Ni, and Cr components of the alloys, and generally discusses specificadditives and modifiers, the amounts and interactions of the modifiers,and the particular benefits that could be expected from them.

[0077] In addition to the materials described above, hydrogen storagematerials for the negative electrode of a NiMH battery may also bechosen from the disordered metal hydride alloy materials that aredescribed in detail in U.S. Pat. No. 5,277,999 (“the '999 Patent”), toOvshinsky and Fetcenko, the disclosure of which is incorporated byreference.

[0078] As stated above, the active hydrogen storage material iscompressed onto a porous metal substrate. Generally, the porous metalsubstrate, includes, but is not limited to, mesh, grid, matte, foil,foam and plate. Preferably, the porous metal substrate used for thenegative electrode is a mesh or grid. The present invention includesnickel metal hydride batteries having negative and positive electrodesthat comprise a porous metal substrate formed from one or more materialsselected from the group consisting of copper, copper alloy, nickelcoated with copper, nickel coated with copper alloy, and mixturesthereof. Preferably, the porous metal substrate is formed from copper orcopper alloy.

[0079] Alkaline batteries represent an extremely harsh operatingenvironment. In order to protect the electrodes from the harshenvironment within the battery, the porous metal substrate formed fromthe materials describe above may be plated with a material that iselectrically conductive yet resistant to corrosion in the batteryenvironment. Examples of materials that can be used to plate thenegative electrode include, but are not limited to, nickel and nickelalloy.

[0080] Using copper or copper alloy to form the porous metal substrateof the negative electrode has several important advantages. Copper is anexcellent electrical conductor. Hence, its use as a substrate materialdecreases the resistance of the negative electrode. This decreases theamount of battery power wasted due to internal dissipation, and therebyprovides a NiMH battery having increased output power.

[0081] Copper is also a malleable metal. Malleability is very importantbecause of the expansion and contraction of the negative electrodesduring charge and discharge cycling of a NiMH battery. The increasedpliability of the substrate helps prevent electrode breakage as a resultof the expansion and contraction, thereby resulting in improved batteryreliability. Further, copper has excellent thermo-conductivity. Ofitself, this fact aids in the temperature management of the batteries ofthe invention. And copper's thermo-conductivity tends to further enhancethe thermo-conductive aspects of the invention described below.

[0082] Increased substrate malleability also means that the substratecan more reliably hold the active hydrogen storage material that iscompressed onto the substrate surface, thereby improving batteryreliability. This also lessens the need to sinter the negativeelectrodes after the storage material is compressed onto the substratesurface, thereby reducing the cost and increasing the speed in which theelectrodes are made.

[0083] Another way to increase the power output from a nickel-metalhydride battery is to increase the conductivity of the battery'spositive electrodes. As in the case of the negative electrodes, this canbe done by appropriately altering the materials from which certainelectrode components are made.

[0084] Generally, the positive electrode of the nickel-metal hydridebattery is formed by pressing a powdered active positive electrodematerial into a porous metal substrate. NiMH batteries generally employa positive electrode having nickel hydroxide as the active material. Thereactions that take place at the positive electrode are as follows:

[0085] The nickel hydroxide positive electrode is described in U.S. Pat.Nos. 5,344,728 and 5,348,822 (which describe stabilized disorderedpositive electrode materials) and U.S. Pat. No. 5,569,563 and U.S. Pat.No. 5,567,549 the disclosures of which are incorporated by reference.

[0086] The porous metal substrate of the positive electrode includes,but is not limited to, mesh, grid, matte, foil, foam and plate.Disclosed herein, is a positive electrode comprising a porous metalsubstrate that is formed from one or more materials selected from thegroup consisting of copper, copper alloy, nickel coated with copper,nickel coated with a copper alloy, and mixtures thereof. Forming thesubstrate from one or more of these materials increases the conductivityof the positive electrodes of the battery. This decreases the amount ofpower wasted due to internal power dissipation, and thereby increasesthe power output of the NiMH battery.

[0087] To protect the positive electrode from the harsh batteryenvironment, the porous metal substrate may be plated with a materialwhich is electrically conductive yet resistant to corrosion in thebattery environment. Preferably, the porous metal substrate may beplated with nickel for protection.

[0088] The conductivity of the positive electrode may be increased inother ways. The conductivity of the positive electrode can be increasedby introducing lines of higher electrical conductivity into the porousmetal substrate. These “current collection lines” are formed so as tohave a higher electrical conductivity than the remainder of thesubstrate and thus provide high conductivity pathways from points remotefrom the current collection tabs of the positive electrodes.

[0089] An embodiment of a positive electrode comprising currentcollection lines is shown in FIG. 4. As shown in FIG. 4, attached to thepositive electrode 1 is a current collecting tab 2. Generally, thecurrent collecting tab 2 is attached to at least one point of thepositive electrode attached along the top of the positive electrodes sothat they may be easily connected to the positive battery terminal ofthe nickel-metal hydride battery. The current collecting tab 2 may beformed of any electrically conducting material which is resistant tocorrosion from the battery environment. Preferably, the currentcollecting tab 2 may be formed of nickel, nickel-plated copper, ornickel-plated copper alloy. Forming the current collecting tab 2 fromeither nickel-plated copper or nickel-plated copper alloy rather thanfrom nickel decreases the resistance of the tab and increases the poweroutput from the battery. Tabs formed from either nickel-plated copper ornickel-plated copper alloy may be connected to the battery terminal vialaser welding.

[0090] As described, the current collecting lines provide highconductivity pathways from points remote from the current collectiontabs. The current collection lines may be configured in many differentways. Preferably, the current collection lines are configured tominimize the resistance of the positive electrodes and allow the currentflowing in the electrode to reach the collecting tabs with minimal lossof power. Because the current collection lines provide high conductivitypathways for the current, the overall conductivity of the positiveelectrodes is increased, thereby reducing the waste of internal powerdissipation and increasing the power output of the battery. Oneembodiment of a configuration of the current collection lines is shownin FIG. 4, where the current collecting lines 3 traverse the positiveelectrode.

[0091] The current collection lines are formed in a porous metalsubstrate which, as discussed above, includes, but is not limited to,mesh, grid, matte, foil, foam and plate. Preferably, the porous metalsubstrate is formed from foam. More preferably, the porous metalsubstrate is formed from nickel foam or nickel plated copper foam.

[0092] The current collection lines may be implemented in many differentways. In one embodiment, the current collection lines comprise densifiedportions of the porous metal substrate. The densified portions of thematerial are more conductive than the remainder of the material. Whenthe substrate is comprised of foam, the current collection lines can beformed (i.e. the material densified) by compressing the appropriateportions of the foam.

[0093] In yet another embodiment, the current collection lines may beformed by conductive powder which is sintered to the porous substrate inthe appropriate configuration. The powder may be formed from one or morematerials selected from the group consisting of copper, copper alloy,nickel-plated copper, nickel-plated copper alloy, nickel, nickel coatedwith copper, and nickel coated with copper alloy, and mixtures thereof.

[0094] Alternately, in another embodiment, the current collection linesmay be formed by first forming densified portions or channels in theporous substrate, and then integrating the conductive wire, ribbon orpowder into these densified portions or channels.

[0095] In other embodiments, the current collection lines are formed byconductive wires and ribbons that are electrically connected to thesubstrate and appropriately placed to minimize the resistance of theelectrodes. The wires or ribbons may be formed from one or morematerials selected from the group consisting of copper, copper alloy,nickel-plated copper, nickel-plated copper alloy, nickel, nickel coatedwith copper, and nickel coated with copper alloy, and mixtures thereof.

[0096] In another embodiment of the present invention, the conductivityof the positive electrodes is further enhanced by the addition ofconductive additives added to the nickel hydroxide active electrodematerial. Such current conducting additives are chosen from the groupconsisting of nickel particles, nickel fibers, graphite particles,nickel plated graphite particles, nickel plated copper particles, nickelplated copper fibers, nickel flakes, and nickel plated copper flakes.

[0097] Another aspect of this invention is a nickel-metal hydridebattery having at least one positive electrode of the type disclosedherein. And yet another aspect of this invention is a nickel-metalhydride battery having at least one negative electrode of the typedisclosed herein.

[0098] In all batteries, heating occurs during charging and discharging.Because internal resistance in NiMH batteries is low, less heat isgenerated than in many prior art types of batteries. Recent experimentaldata indicates that during overcharge the heat generated by therecombination of oxygen, while not significant in small consumerbatteries, could become a problem the batteries of the HEV systemdescribed herein.

[0099] Heat would become a particular problem in sealed NiMH batterieshaving pasted electrodes and a plastic case in an HEV systemapplication. Recent analysis using a pasted electrode and a plastic casehas shown that the heat generated during overcharge is essentiallytrapped in the cell where temperatures can reach 80° C. In NiMHbatteries, excessive heat decreases performance and decreases cell lifedue to separator and seal degradation as well as accelerated degradationof the nickel hydroxide and metal hydride active materials.

[0100] Many NiMH batteries currently on the market use pasted metalhydride electrodes in order to achieve sufficient gas recombinationrates and to protect the base alloy from oxidation and corrosion. Thepasted electrode typically mixes the active material powder with plasticbinders, such as Teflon, and other nonconductive hydrophobic materialsto the electrode. An unintended consequence of this process is asignificant reduction in the thermal conductivity of the electrodestructure as compared to a structure of the present invention whichconsists essentially of a 100% conductive active material pressed onto aconductive substrate.

[0101] In an embodiment of the sealed NiMH batteries that are acomponent of the HEV system of the present invention, the buildup ofheat generated during overcharge is avoided by using a cell bundle ofthermally conductive NiMH electrode material. This thermally conductiveNiMH electrode material that contains NiMH particles in intimate contactwith each other. Oxygen gas generated during overcharge recombines toform water and heat at the surface of these particles. In the presentinvention, this heat follows the negative electrode material to thecurrent collector and then to the surface of the case. The thermalefficiency of the bundle of thermally conductive NiMH electrode materialcan be further improved if this electrode bundle is in thermal contactwith a battery case that is also of high thermal conductivity.

[0102] In such thermally efficient batteries, the NiMH negativeelectrode material is preferably a sintered electrode such as describedin U.S. Pat. Nos. 4,765,598; 4,820,481; and 4,915,898 (the contents ofwhich are incorporated by reference) sintered so that the NiMH particlesare in intimate contact with each other.

[0103] Yet another aspect of the present invention is a fluid-cooledbattery pack systems (as used herein the terms “battery pack” or “pack”refer to two or more electrically interconnected battery modules).Again, it should be noted that during cycling of the batteries theygenerate large amounts of waste heat. This is particularly true duringcharging of the batteries, which in a hybrid vehicle is nearly constant.This excess heat can be deleterious and even catastrophic to the batterysystem. Some of the negative characteristics which are encountered whenthe battery pack systems have no or improper thermal managementinclude: 1) substantially lower capacity and power; 2) substantiallyincreased self discharge; 3) imbalanced temperatures between batteriesand modules leading to battery abuse; and 4) lowered cycle life of thebatteries. Therefore, it is clear that to be optimally useful thebattery pack systems need proper thermal management.

[0104] Some of the factors to be considered in the thermal management ofbattery pack systems are 1) all batteries and modules must be keptcooler than 65° C. to avoid permanent damage to the batteries; 2) allbatteries and modules must be kept cooler than 55° C. to get at least80% of the battery's rated performance; 3) all batteries and modulesmust be kept cooler than 45° C. to achieve maximum cycle life; and 4)the temperature difference between individual batteries and batterymodules must be kept below 8° C. for optimal performance. It should benoted that the improvements in the instant invention regulate thetemperature difference between batteries to less than about 2° C.

[0105] The thermal management of the battery pack system must provideadequate cooling to insure optimal performance and durability of theNi—MH batteries in a wide variety of operating conditions. Ambienttemperatures in the U.S. lie in a wide range from at least −30° C. to43° C. in the lower 49 states. It is necessary to achieve operationalusefulness of the battery packs under this ambient temperature rangewhile maintaining, the batteries in their optimal performance range ofabout −1° C. to 38° C.

[0106] Nickel-metal hydride batteries show charge efficiency performancedegradation at extreme high temperatures over 43° C. due to problemsresulting from oxygen evolution at the nickel positive electrode. Toavoid these inefficiencies the battery temperature during charge shouldideally be held below 43° C. Nickel-metal hydride batteries also showpower performance degradation at temperatures below about −1° C. due todegraded performance in the negative electrode. To avoid low power, thebattery temperature should be held above about −1° C. during discharge.

[0107] As alluded to above, in addition to degraded performance at highand low temperatures, detrimental effects can occur as a result oftemperature differentials between batteries within a module duringcharge. Large temperature differentials cause imbalances in chargeefficiencies of the batteries, which, in turn, can producestate-of-charge imbalances resulting in lowered capacity performance andpotentially leading to significant overcharge and overdischarge abuse.To avoid these problems the temperature differential between thebatteries should be controlled to less than 8° C. and preferably lessthan 5° C.

[0108] Other factors in the design of a fluid-cooled battery pack systeminclude mechanical considerations. For instance, battery and modulepacking densities must be as high as possible to conserve space in theend product. Additionally, anything added to the battery pack system toprovide for thermal management ultimately reduces the overall energydensity of the battery system since it does not contribute directly tothe electrochemical capacity of the batteries themselves. In order tomeet these and other requirements the instant inventors have designedthe fluid-cooled battery pack system of the instant invention.

[0109] In its most basic form (an embodiment shown in FIG. 5) theinstant fluid-cooled battery pack system 39 includes: 1) a battery-packcase 40 having at least one coolant inlet 41 and at least one coolantoutlet 42; 2) at least one battery module 32 disposed and positionedwithin the case 40 such that the battery module 32 is spaced from thecase walls and from any other battery modules 32 within the case 40 toform coolant flow channels 43 along at least one surface of the bundledbatteries, the width of the coolant flow channels 43 is optimally sizedto allow for maximum heat transfer, through convective, conductive andradiative heat transfer mechanisms, from the batteries to the coolant;and 3) at least one coolant transport means 44 which causes the coolantto enter the coolant inlet means 41 of the case 40, to flow through thecoolant flow channels 43 and to exit through the coolant outlet means 42of the case 40. Preferably, and more realistically, the battery packsystem 39 includes a plurality of battery modules 32, typically from 2to 100 modules, arranged in a 2 or 3 dimensional matrix configurationwithin the case. The matrix configuration allows for high packingdensity while still allowing coolant to flow across at least one surfaceof each of the battery modules 32.

[0110] The battery-pack case 40 is preferably formed from anelectrically insulating material. More preferably the case 40 is formedfrom a light weight, durable, electrically insulating polymer material.The material should be electrically insulating so that the batteries andmodules do not short if the case touches them. Also, the material shouldbe light weight to increase overall pack energy density. Finally, thematerial should be durable and capable of withstanding the rigors of thebattery pack's ultimate use. The battery pack case 40 includes one ormore coolant inlets 41 and outlets 42, which may be specialized fluidports, where required, but are preferably merely holes in the batterypack case 40 through which cooling-air enters and exits the batterypack.

[0111] The fluid cooled battery-pack system 39 is designed to useelectrically-insulating coolant, which may be either gaseous or liquid.Preferably the coolant is gaseous and more preferably the coolant isair. When air is used as the coolant, the coolant transport means 44 ispreferably a forced-air blower, and more preferably a blower whichprovides an air flow rate of between 1-3 SCFM of air per cell in thepack.

[0112] The blowers do not need to continuously force cooling air intothe battery pack, but may be controlled so as to maintain the batterypack temperatures within the optimal levels. Fan control to turn the fanon and off and preferably to control the speed of the fan is needed toprovide for efficient cooling during charging, driving, and idle stands.Typically, cooling is most critical during charge, but is also neededduring aggressive driving. Fan speed is controlled on the basis of thetemperature differential between the battery pack and ambient, as wellas on the basis of absolute temperature, the latter so as not to coolthe: battery when already it is already cold or so as to provide extracooling when the battery nears the top of its ideal temperature range.For nickel-metal hydride batteries, fans are also needed in idle periodsafter charge. Intermittent cooling is needed to provide for efficientcooling under this condition and results in net energy savings bykeeping self discharge rates below fan power consumption. A typicalresult shows a fan on time of 2.4 hours after the initial post chargecool down. Typically the normal fan control procedure (described below)works well in this scenario. Fan control allows for the use of powerfulfans for efficient cooling when needed without the consumption of fullfan power at all times, thus keeping energy efficiency high. The use ofmore powerful fans is beneficial in terms of maintaining optimal packtemperature which aids in optimization of pack performance and life.

[0113] One example of a fan control procedure provides that, if themaximum battery temperature is over 30° C. and the ambient temperatureis lower (preferably 5° C. or more lower) than the maximum batterytemperature then the fans will turn on and circulate cooler air into thecoolant channels.

[0114] The flow rate and pressure of the cooling fluid needs to besufficient to provide sufficient heat capacity and steady state removalof heat at the maximum anticipated sustained heat generation rate toresult in an acceptable temperature rise. In typical Ni-MR batterypacks, with 5-10 W per cell generated during overcharge (maximum heatgeneration), a flow rate df 1-3 CFM of air per cell is needed to provideadequate cooling simply on the basis of the heat capacity of air andachieving an acceptable temperature rise. Radial blower type fans may beused to provide the most effective airflow for thermal management. Thisis due to the higher air pressure generated by these fan types ascontrasted with that generated by axial fans. Generally, a pressure dropof at least 0.5″ of water is required at the operating point of the fanas installed in the pack. To produce this pressure drop at high flowrates generally requires a fan static pressure capability of 1.5″ to 3″of water.

[0115] In addition to using the fans to cool the battery pack when it ishot, the fans can heat the battery pack when it is too cold. That is, ifthe battery pack is below its minimum optimal temperature, and theambient air is warmer than the battery pack, the fans may be turned onto draw warmer ambient air into the battery pack. The warmer air thentransfers its thermal energy to the battery pack and warms it to atleast the low end of the optimal range of temperature.

[0116] One or more coolant transport means 44 can be positioned at thecoolant inlet 41 to force fresh coolant into the battery pack case 40,through coolant flow channels 43, and out of the coolant outlet 42.Alternatively, one or more coolant transport means 44 can be positionedat the coolant outlet 42 to draw heated coolant out of the battery packcase 40, causing fresh coolant to be drawn into the battery pack case 40via the coolant inlet 41, and to flow through the coolant flow channels43.

[0117] The coolant may flow parallel to the longest dimension of thecoolant flow channels 43 (i.e. in the direction of the length of thebattery modules) or, alternatively, it may flow perpendicular to thelongest dimension of said coolant flow channels 43, (i.e. in thedirection of the height of the batteries as it flows through the coolingchannels 43, the coolant heats up. Therefore, it is preferable that thefluid flow perpendicular to the longest dimension of the coolingchannels 43. This is because as the coolant heats up, the temperaturedifference between the batteries and the coolant decreases andtherefore, the cooling rate also decreases. Thus the total heatdissipation is lowered. To minimize this effect, the coolant flow pathshould be the shorter of the two, i.e. along the height of thebatteries.

[0118] While air is the most preferred coolant (since it is readilyavailable and easy to transport into and out of the case) other gasesand even liquids may be used. Particularly, liquid coolants such asFreon or ethylene glycol, as well as other commercially availablefluorocarbon and non-fluorocarbon based materials may be used. Whenthese other gases or liquids are used as the coolant, the coolanttransport means 44 may preferably be a pump. When using coolants otherthan air, the coolant transport means may preferably include a coolantreturn line attached to the coolant outlet 42 which recycles heatedcoolant to a coolant reservoir (not shown) from which it is transferredto a coolant heat exchanger (not shown) to extract heat therefrom andfinally redelivered to the coolant pump 44 for reuse in the cooling ofthe battery pack 39.

[0119] The optimized coolant flow channel width incorporates manydifferent factors. Some of these factors include the number ofbatteries, their energy density and capacity, their charge and dischargerates, the direction, velocity and volumetric flow rate of the coolant,the heat capacity of the coolant and others. It has been found thatindependent of most of these factors, it is important to design thecooling channels 43 to impede or retard the cooling fluid flow volume asit passes between the modules. Ideally, the retardation in flow ispredominantly due to friction with the cell cooling surfaces, whichresults in a flow reduction of 5 to 30% in flow volume. When the gapsbetween modules form the major flow restriction in the cooling fluidhandling system, this produces a uniform and roughly equal cooling fluidflow volume in the gaps between all modules, resulting in even cooling,and reducing the influence of other flow restrictions (such as inlets orexits) which could otherwise produce nonuniform flow between themodules. Furthermore, the same area of each cell is exposed to coolingfluid with similar velocity and temperature.

[0120] Battery modules are arranged for efficient cooling of batterycells by maximizing the cooling fluid velocity in order to achieve ahigh heat transfer coefficient between the cell surface and the coolingfluid. This is achieved by narrowing the intermodule gap to the pointthat the cooling fluid also helps raise the heat transfer coefficient asthe shorter distance for heat transfer in the cooling fluid raises thecell to fluid temperature gradient.

[0121] The optimal coolant flow channel width depends on the length ofthe flow path in the direction of flow as well as on the area of thecoolant flow channel in the plane perpendicular to the flow of thecoolant. There is a weaker dependence of optimal gap on the fancharacteristics. For air, the width of the coolant flow channels 43 isbetween about 0.3-12 mm, preferably between 1-9 mm, and most preferablybetween 3-8 mm. For vertical air flow across a module 7 inches high, theoptimal achievable mean module spacing (width of the coolant flowchannels 43) is about 3-4 mm (105 mm centerline spacing). For horizontalair flow lengthwise across 4 modules 16 inches long in a row for a totaldistance of 64 inches, the optimal achievable mean module spacing (widthof the coolant flow channels 43) is about 7-8 mm (109 mm centerlinespacing). Slightly closer intermodule spacing at the far end of this rowwill result in a higher airflow rate and consequently a higher heattransfer coefficient, thus compensating for the higher air temperaturedownstream. A secondary inlet or series of inlets partway along thehorizontal coolant flow path can also be used as a means of introducingadditional coolant, thus making the heat transfer between the batterycells and the coolant more uniform along the entire flow path.

[0122] In should be noted that the term “centerline spacing” issometimes used synonymously with coolant flow channel width. The reasonfor this is that the quoted coolant flow channel widths are averagenumbers. The reason for this averaging is that the sides of the batterymodules which form the flow channels 43 are not uniformly flat and even,the banding which binds the modules together and the sides of thebatteries themselves cause the actual channel width to vary along itslength. Therefore; it is sometimes easier to describe the width in termsfor the spacing between the centers of the individual modules, i.e. thecenterline width, which changes for batteries of different sizes.Therefore, it is generically more useful to discuss an average channelwidth, which applies to battery modules regardless of the actual batterysize used therein.

[0123] To assist in achieving and maintaining the proper spacing of themodules within the pack case and to provide electrical isolation betweenthe modules, each module includes coolant-flow-channel spacers 37 whichhold the modules 32 at the optimal distance from any other modules 32and from the battery pack case 40 to form the coolant flow channels 43.As disclosed above, the coolant-flow-channel spacers 37 are preferablypositioned at the top and bottom of the battery modules 32, providingprotection to the corners, of the modules 32, the battery terminals 7, 8and the electrical interconnects 25. More importantly, tabs on the sidesof the spacers 38 hold the modules at the optimal distance apart. Thespacers 37 are preferably formed from a light weight, electricallynon-conductive material, such as a durable polymer. Also, it isimportant to the overall pack energy density that the spacers include aslittle total material as possible to perform the required function andstill be as light as possible.

[0124] As mentioned above Ni-MH batteries operate best in a specifictemperature range. While the cooling system described above enables thebattery pack systems of the instant invention to maintain operatingtemperatures lower than the high temperature limit of the optimal range(and sometimes to operate above the lower temperature limit of theoptimal range, if the ambient air temperature is both warmer than thebattery and warmer than the lower temperature limit of the optimalrange), there are still times when the battery system will be colderthan the lower limit of optimal temperature range. Therefore, there is aneed to somehow provide variable thermal insulation to some or all or ofthe batteries and modules in the battery pack system.

[0125] In addition to the cooling systems described above, another wayto thermally control the battery pack systems of the instant inventionis by the use of temperature dependant charging regimens. Temperaturedependent charge regimens allow for efficient charging under a varietyof ambient temperature conditions. One method involves charging thebatteries to a continuously updated temperature dependent voltage lidwhich is held until the current drops to a specified value after which aspecified charge input is applied at constant current. Another methodinvolves a series of decreasing constant current or constant power stepsto a temperature compensated voltage limit followed by a specifiedcharge input applied at a constant current or power. Another methodinvolves a series of decreasing constant current or constant power stepsterminated by a maximum measured rate of temperature rise followed by aspecified charge input applied at a constant current or power. Use oftemperature dependant voltage lids ensures even capacity over a widerange of temperatures and ensures that charge completion occurs withminimal temperature rise. For example, use of fixed voltage charge lidsresults in an 8° C. temperature rise. Absolute charge temperature limits(60° C.) are required for this battery to avoid severe overheating whichcan occur in the case of simultaneous failure of charger and coolingsystem. Detection of rate of change of voltage with respect to time(dV/dt) on a pack or module basis allows a negative value of dV/dt toserve as a charge terminator. This can prevent excessive overcharge andimproves battery operating efficiency as well as serving as anadditional safety limit.

[0126] As discussed above, in addition to having an upper limit on theoperational temperature range of the instant batteries, there is also alower limit. As also discussed ab can be used as a heating system.However, it is much more likely that if the battery pack temperature islow, the ambient temperature will also be low, and probably lower thanthe battery pack temperature. Therefore, there will be times duringoperational use of the battery pack system when it will be advantageousto thermally insulate the batteries from the ambient. However, the needfor thermal insulation will not be constant and may vary dramatically inonly a matter of a very short time period. Therefore, the thermalinsulation need will also be variable.

[0127] In order to accommodate this variable need for thermalinsulation, the instant inventors have devised a means for providingvariable thermal insulation. The inventive variable thermal insulationmeans can be used on individual batteries, battery modules and batterypack systems alike.

[0128] In its most basic form, the means provides variable thermalinsulation to at least that portion of the rechargeable battery systemwhich is most directly exposed to said ambient thermal condition, so asto maintain the temperature of the rechargeable battery system withinthe desired operating range thereof under variable ambient conditions.

[0129] To provide this variable thermal insulation, the inventors havecombined temperature sensor means and compressible thermal insulationmeans. When the temperature sensor indicates that the ambient is cold,the thermal insulation is positioned in the needed areas to insulatedthe affected areas of the battery, module or battery pack system. Whenthe ambient is warmer, the temperature sensor causes the thermalinsulation to be partly or wholly compressed such that the insulationfactor provided to the battery system by the compressible insulation ispartially or totally eliminated.

[0130] The thermal sensors may be electronics which variably increasesor decreases the insulation. The thermal sensors may be electronicsensors which feed information to piston devices which variablyincreases or decreases the compression upon a compressible foam or fiberinsulation. Alternatively, (and more preferably from an electricalenergy utilization and mechanical reliability point of view,) the sensorand compression devices may be combined in a single mechanical deviceswhich causes variable compression upon the thermal insulation in directreaction to the ambient thermal condition. Such a combinedsensor/compression device and be formed from a bimetallic material suchas the strips used in thermostats. Under low ambient temperatures, thebimetallic device will allow the thermal insulation to expand into placeto protect the battery system from the cold ambient conditions, but whenthe temperature of the battery or ambient rises, the bimetal devicecompresses the insulation to remove its insulating effect from thebattery system.

[0131] While the variable thermal insulation can be used to completelysurround the entire battery, module or battery pack system, it is notalways necessary to do so. The variable thermal insulation can be justas effective when it only insulates the problems spots of the system.For example, in the battery modules and pack systems of the instantinvention, which employ ribbed end plates, it may only be necessary formodules which are most directly influenced by low temperature ambientconditions. These ambient conditions may cause large temperatureimbalances between the batteries of the module(s) and as a resultdegrade the performance of the module or pack system. By providingvariable insulation to the affected end(s) of the module(s) thetemperature differential between the batteries can be reduced oreliminated and the overall temperature of the module(s) can becontrolled.

[0132] The battery case of the present invention is preferablyconstructed of a metallic material such as steel. In a preferredembodiment, the metallic material is stamped, embossed, or shaped toform pressure containing surfaces that counter the internal pressure ofthe sealed battery and thus prevent bulging of the case. Bulging isdetrimental to individual batteries because it alters the electrolytedistribution and spatial orientation of the electrodes and separators.Alternatively, a cylindrical metallic case can be used.

[0133] In all commercial, sealed, metal hydride batteries, the positiveelectrode is designed to be capacity limited. This means that thepositive electrode reaches full charge before the negative electrode.When this occurs, oxygen gas evolves at the positive electrode inproportion to the current supplied. In overcharge, ail current isproducing oxygen gas. In order for the battery to remain sealed, theremust be a recombination mechanism for the oxygen gas that is evolved.

[0134] One recombination mechanism involves the diffusion of oxygen gasgenerated at the positive electrode through the separator to the surfaceof the metal hydride electrode where it recombines. The rate limitingstep of this mechanism is the diffusion of the oxygen gas through theelectrolyte film to reach the surface of the metal electrode. Once theoxygen gas reaches the surface of the electrode, gas recombination israpid. If, however, the oxygen must diffuse through a thick film ofelectrolyte on the surface of the negative electrode, gas recombinationrates will be slowed significantly. Thus, the rate of the reaction isproportional to the amount of electrolyte at the surface of theelectrode. This amount is referred to as the film thickness of theelectrolyte.

[0135] An additional aspect of the present invention is a hydrophobictreatment that acts to significantly decrease this film thickness. Thedescribed hydrophobic treatment produces a thin electrolyte filmprecisely where it is the most beneficial, at the surface of the metalhydride negative electrode.

[0136] The present invention recognizes that a hydrophobic treatment ismost important at the outer surfaces of the metal hydride electrode and,in particular, at the metal-electrolyte interface. The present inventioninvolves a small thin coating on the surface of either the negativeelectrode or the surface of the separator in contact with the negativeelectrode. This provides a degree of hydrophobicity where it is needed.The coating of the present invention has a tremendous advantage over theprior art because while the surface of the negative electrode isrendered hydrophobic, the interior remains unaffected. This is becausethe gas state combination occurs only on the outer surface of thenegative. Thus the presence of a hydrophobic interior, as in the priorart, is actually detrimental to electrolyte absorption rates, overallelectrolyte absorption, power, cycle life, low temperature, and otherperformance parameters related to the negative electrode.

[0137] It is common for manufacturers of NiMH batteries to mix anorganic binder, such as polytetrafluoroethylene (PTFE), with the metalhydride negative electrode alloy powder to prevent cracking and loss ofthe metal hydride materials. Such a formulation results in hydrophobicmaterial in the bulk of the electrode (thereby increasing electroderesistance) and the resulting hydrophobicity reduces the effectivenessof the initial etch in removing surface impurities. In addition,hydrophobic binders in the bulk reduce electrolyte absorption whichlowers cycle life, decreases conductivity, and takes up space.

[0138] Contrary to the teachings of the present application, JP A4-277467 teaches making the electrode surface hydrophilic by spraying itwith alcohol in order to improve the internal pressure.

[0139] Unexpectedly, the inventors of the present invention found thatin addition to using a negative electrode where the surface facing theseparator had been treated to render it hydrophobic it was also possibleto attain similar results by using a separator and an untreated negativeelectrode where the surface of separator facing the negative electrodehad been treated to make it hydrophobic. Without wishing to be bound bytheory, it is believed that hydrophobic material on the surface of theseparator facing the negative electrode is in such intimate contact withthe negative electrode that it reduces the film thickness of theelectrolyte on the electrode as if the negative electrode itself hadbeen treated.

[0140] While at first glance it might appear advantageous to treat thesurface of the negative electrode and the surface of the separatorfacing the negative electrode to render them both hydrophobic, theinventors have found that this is not effective. When both surfaces aretreated, the thickness of the resulting hydrophobic material is so greatthat oxygen recombination is significantly slowed.

[0141] This is the case in JP A 5-242908 which describes using a layerof PTFE between the negative electrode and the separator (effectivelytreating both, the surface of the negative electrode and the surface ofthe separator). While JP A 5-242908 discusses the advantages of oxygenrecombination on the electrode, a table in JP A 5-242908 shows cellpressures reduced only to a range of from 81-114 psi. (The temperatureof the cells is not indicated.) These pressures are much greater thanthe pressures in cells of the present invention, as shown in Table 1,below. The use of a coated electrode or separator as described in thepresent invention, avoids the problems inherent in an extra layer. Acoated electrode according to the present invention simplifies andreduces the cost of assembly because the coating can be applied prior toassembly. Using a thin film layer of PTFE between the separator and theelectrode would generate a variety of problems during assembly. Forexample, stretching could produce non-uniform porosity that wouldproduce non-uniform gas recombination and diffusion rates. A coatedelectrode effectively permits the use of a much thinner hydrophobiclayer so that uniform and rapid oxygen recombination is encouragedwithout impeding diffusion rates.

[0142] The present invention is effective with all types of batterysystems in which oxygen is evolved at the positive electrode duringovercharge. The present invention is particularly useful with nickelmetal hydride systems (such as the ones commonly referred to as Ovonicsystems, AB₂ systems, AB₅ systems, and mischmetal systems). Mostparticularly, the present invention is useful with alloys of the typedescribed in copending U.S. patent application Ser. No. 08/259,793,filed Jun. 14, 1994, titled ELECTROCHEMICAL HYDROGEN STORAGE ALLOYS ANDBATTERIES FABRICATED FROM MG CONTAINING BASE ALLOYS.

[0143] The present invention is particularly useful in batteries of theHEV system of the present invention because such batteries must undergonumerous quick charge/discharge cycles. This is because quick chargingresults in earlier oxygen gas generation. In batteries that are beingquick charged it is also important that the oxygen generated duringthese periods of overcharge be recombined quickly to prevent venting andloss of capacity. In addition, the present invention is particularlyeffective at high temperatures, which increases its usefulness inbatteries that are going to be quick charged. Obviously, the use of thethermal management system described above will increase the efficienciesof such gas recombination.

[0144] While a 1% PTFE suspension is specifically demonstrated below,any suitable hydrophobic treatment may be used that will reduce the filmthickness of the electrolyte at the surface of the metal hydridenegative electrode. Cells of the present invention suffer no performancetradeoffs in cycle life, power, charge retention, or low temperatureperformance as a result of the hydrophobic treatment.

[0145] While any metal hydride alloy may be used, cells of the presentinvention are preferably fabricated from low pressure negative electrodematerials such as those described in U.S. Pat. No. 5,277,999, thecontents of which are incorporated by reference. Such hydrogen storagealloys have the composition

(Base Alloy)_(a)Co_(b)Mn_(c)Al_(d)Fe_(e)La_(f)Mo_(g)

[0146] where Base Alloy represents a disordered multicomponent alloyhaving at least one structure selected from the group consisting ofamorphous, microcrystalline, polycrystalline (lacking long-rangecompositional order with three or more phases of the polycrystallinestructure), and any combination of these structures; b is 0 to 7.5atomic percent, preferably 4 to 7 atomic percent; c is 0 to 8.5 atomicpercent, preferably 6 to 8 atomic percent; d is 0 to 2.5 atomic percent,preferably 0.1 to 2 atomic percent; e is 0 to 6 atomic percent,preferably 1 to 3 atomic percent or 5.3 to 6 atomic percent; f is 0 to4.5 atomic percent, preferably 1 to 4 atomic percent; g is 0 to 6.5atomic percent, preferably 0.1 to 6 atomic percent, most preferablyabout 6 atomic percent; b+c+d+e+f+g>0; and a+b+c+d+e+f+g=100 atomicpercent. A preferred formulation of this Base Alloy contains 0.1 to 60atomic percent Ti, 0.1 to 25 atomic percent Zr, 0.1 to 60 atomic percentV, 0.1 to 57 atomic percent Ni, and 0.1 to 56 atomic percent Cr and b is4 to 7 atomic percent; c is 6 to 8 atomic percent; d is 0.1 to 2 atomicpercent; e is 1 to 2 atomic percent; f is 0.1 to 4 atomic percent; and gis 0.1 to 6 atomic percent; b+c+d+e+f+g>0; and a+b+c+d+e+f+g=100 atomicpercent.

[0147] While any positive electrode material compatible with metalhydroxide negative electrodes may be used (such as nickel hydroxide),the positive electrodes of the present invention are preferably of thetype described in U.S. Pat. Nos. 5,344,782, 5,348,822, 5,523,182,5,569,562, and 5,567,549. These electrodes are locally ordered,disordered, high capacity, long cycle life positive electrodescomprising a solid solution nickel hydroxide electrode material having amultiphase structure and at least one compositional modifier to promotethe multiphase structure. The multiphase posi-phase unit cell comprisingspacedly disposed plates with at least one ion incorporated around theplates, the plates having a range of stable intersheet distancescorresponding to a 2⁺ oxidation state and a 3.5^(+,) or greater,oxidation state. The at least one compositional modifier is a metal, ametallic oxide, a metallic oxide alloy, a metal hydride, and/or a metalhydride alloy. Preferably the at least one compositional modifier ischosen from the group consisting of Al, Bi, Co, Cr, Cu, Fe, Ln, LaH₃,Mn, Ru, Sb, Sn, TiH₂, TiO, Zn.

[0148] The separators and bags of the present material are made frommaterial described in detail in U.S. Pat. No. 5,330,861, the contents ofwhich are incorporated by reference. Described in detail in thisapplication are electrolyte retentive nylon and wettable polypropylenematerials that are non-reactive with H₂ gas and alkaline electrolyte.The retentive nylon material is capable of absorbing and retaining moreelectrolyte solution than standard nylon separators. The wettablepolypropylene separators are grafted polypropylene material that retainand absorb electrolyte so that particles, barbs, and residues are notproduced. Grafted polypropylene material is preferably used for both theseparators and the bags of the cells of the present invention.

[0149] While the improvements of the battery electrodes described hereinare directed toward both the positive and the negative electrodes, thisis in no way intended to be limiting. Thus the formation of batteries ofthe invention comprising sintered negative electrodes combined withenhanced conductivity positive electrodes, or prior art pasted negativeelectrodes combined with enhanced conductivity positive electrodes, orenhanced conductivity negative electrodes combined with prior artpositive electrodes, or enhanced conductivity negative electrodescombined with enhanced conductivity positive electrodes are all intendedto be within the scope of the present invention. (The phrase “enhancedconductivity” as used herein is intended to specifically refer to thenegative or positive electrodes of the batteries of the presentinvention.)

EXAMPLES Example 1

[0150] Cells embodying those of the present HEV system and those of theprior art were constructed and tested. These cells are described inTable 1, below. TABLE 1 Comparison HEV Prototype HEV Optimized Prototypepower density (W/L) 1300 1600 2700 specific power (W/kg) 600 600 1000energy density (Wh/L) 120 190 160 specific energy (Wh/Kg) 55 70 60negative electrode pasted Cu substrate Cu substrate, thin electrodesconstruction negative current collector nickel copper copper negativealloy composition misch metal V₁₈Ti₁₅Zr₁₈Ni₂₉Cr₅Co₇Mn₈V₁₈Ti₁₅Zr₁₈Ni₂₉Cr₅Co₇Mn₈ positive electrode pasted Ni(OH)₂ pastedγ-phase Ni(OH)₂ pasted γ-phase Ni(OH)₂ with thin thick conductiveadditives thin separator polypropylene thin polypropylene thinpolypropylene thin case plastic stainless steel stainless steel aspectratio square square square top plastic stainless steel stainless steeltabs thick thick/laser welded thick/laser welded

[0151] As can be seen from Table 1, the embodiments of the invention,the HEV prototype cells and REV optimized prototype cells representimprovements over the comparison cells fabricated in accordance with theprior art. In particular, the HEV optimized prototype embodies the mostdramatic improvements.

[0152] Table 1 shows that the Cu substrate of the invention provides theimproved current conduction essential for reducing internal resistance.Similarly, the use of conductive additives, such as nickel fibers,nickel plated graphite particles, nickel plated copper particles, nickelplated copper fibers, or the use of a conductive mat embedded in thepasted negative electrode material all contribute to the conductivity ofthe positive electrode. In addition, the use of thick tabs that arelaser welded assures that the improved conductivity of the electrodes isnot lost at the collection points. Alternately, negative electrodeshaving the composition Ti₁₀Zr₂₈Ni₃₆Cr₅Co₅Mn₁₆ may be used.

Example 2

[0153] The impact of the thermally conductive electrodes of the presentinvention can be evaluated independently. Comparison cells and thermallyconductive cells were fabricated as described in Table 2. TABLE 2Comparison Cell Thermally conductive cells capacity 100 Ah 100 Ah energydensity ≈70 Wh/kg ≈70 Wh/kg negative electrode pasted sintered,compacted construction negative alloy misch metalV₁₈Ti₁₅Zr₁₈Ni₂₉Cr₅Co₇Mn₈ composition positive electrode Ni(OH)₂ pastedonto Ni(OH)₂ pasted onto foam substrate foam substrate case plasticstainless steel top plastic stainless steel temperature after 80° C. 34°C. cycling (charge/ discharge cycling at C/10 overcharge to 120% ofcapacity

Example 3

[0154] Cells (1-7 in Table 3, below) were fabricated as described inU.S. Pat. No. 5,330,861 using a high loft polypropylene separator andnegative electrode alloy having the following composition:

V₁₈Ti₁₅Zr₁₈Ni₂₉Cr₅Co₇Mn₈

[0155] except that the separators were sprayed with 1% aqueous solutionsof PTFE on the side facing the negative electrode prior to assemblingthe cell. The control cells (designated C1-C7 in Table 1, below) wereassembled using untreated separators.

[0156] These cells were charged and discharged at the indicatedtemperatures. The cells having the 1% PTFE coating on the surface of theseparator demonstrated a consistent pressure reduction. As can be seen,this effect is even more pronounced at elevated temperatures andrepresents a significant improvement over the prior art. Table 1 alsoshows that cells of the present invention suffer no tradeoffs in termsof capacity. TABLE 3 Overcharge Temperature (° C.) Pressure (psi)Capacity (Ah) C1 0 32 4.77 C2 10 39 4.58 C3 20 89 4.46 C4 30 113 4.53 C540 136 4.53 C6 50 175 4.45 C7 60 138 3.97 1% Teflon 1 0 46 4.76 2 10 444.45 3 20 42 4.47 4 30 47 4.52 5 40 55 4.54 6 50 75 4.49 7 60 63 4.02

[0157] It is obvious to those skilled in the art that additionalcombinations of the components described above can be made withoutdeparting from spirit and scope of the present invention. For example,extensive addition of conductive components such as metallic nickel orcopper powder to a pasted electrode is anticipated. The discussion anddescription of this specification are merely illustrative of particularembodiments of the invention and are not meant as limitations upon theinvention. It is the following claims, including all equivalents, thatdefine the scope of the invention.

[0158] While the invention has been described in connection withpreferred embodiments and procedures, it is to be understood that it isnot intended to limit the invention to the preferred embodiments andprocedures. On the contrary, it is intended to cover all alternatives,modifications and equivalence which may be included within the spiritand scope of the invention as defined by the claims below.

What is claimed is:
 1. A hybrid electric vehicle drive system comprisinga combustion engine, an electric motor, and at least one nickel metalhydride battery module forming a power source for providing electricpower to said electric motor, said at least one nickel metal batterymodule having a peak power density in relation to energy density asdefined by: P>1,420−16E where P is the peak power density as measured inWatts/kilogram and E is the energy density as measured inWatt-hours/kilogram.
 2. A hybrid electric vehicle drive system as setforth in claim 1 including means for connecting and disconnecting saidcombustion engine and: said electric motor in driving relationship tosaid electric vehicle.
 3. A hybrid electric vehicle drive system as setforth in claim 2 including control means for operating said batterypower module in a charge depleting mode.
 4. A hybrid electric vehicledrive system as set forth in claim 2 including control means foroperating said battery power module in a charge sustaining mode.
 5. Ahybrid electric vehicle drive system as set forth in claim 1 whereinsaid peak power density is at least 600 W/Kg for an energy density ofleast 70 Wh/Kg.
 6. A hybrid electric vehicle drive system as set forthin claim 1 wherein said peak power density is at least 550 W/Kg for anenergy density of least 55 Wh/Kg.
 7. A hybrid electric vehicle drivesystem as set forth in claim 1 wherein said peak power density is atleast 600 W/Kg for an energy density of least 50 Wh/Kg.
 8. A hybridelectric vehicle drive system as set forth in claim 1 wherein saidbattery modules comprise electrodes of high electrical conductivity. 9.A hybrid electric vehicle drive system as set forth in claim 1 whereinsaid high electrical conductivity electrodes are formed substantially ofcopper.
 10. A hybrid electric vehicle incorporating an integratedpropulsion system comprising: a power system comprising a combustionengine and an electric motor, nickel metal hydride batteries configuredfor maximum peak power density and high energy density coupled to saidpower system, and power controlling means governing said power systemand configured for optimum operation of said combustion engine and saidelectric motor.
 11. The hybrid electric vehicle incorporating anintegrated propulsion system of claim 10, further comprising: aregenerative braking system coupled to said power controlling means andproviding charging current for said nickel metal hydride batteries. 12.The hybrid electric vehicle incorporating an integrated propulsionsystem of claim 10, where said nickel-metal hydride batteries havenegative electrodes, or positive electrodes, or negative and positiveelectrodes comprising: powdered active materials pressed into a porousmetal substrate, said porous metal substrate selected from the groupconsisting of copper, copper alloy, nickel coated with copper, andnickel coated with copper alloy.
 13. The hybrid electric vehicleincorporating an integrated propulsion system of claim 10, where saidnickel-metal hydride batteries have a power density of ≧1500 W/L. 14.The hybrid electric vehicle incorporating an integrated propulsionsystem of claim 10, where said nickel-metal hydride batteries have aspecific power of >600 W/kg at an energy density of at least 70 Wh/Kg.15. The hybrid electric vehicle incorporating an integrated propulsionsystem of claim 10, where said nickel-metal hydride batteries have anenergy density≧150 Wh/L.
 16. The integrated propulsion system for ahybrid electric vehicle of claim 12, wherein said negative electrodes,positive electrodes, or negative and positive electrodes have at leastone electrode tab attached to thereto and said electrode tab is directlyattached to said porous metal substrate via a low electrical-resistanceconnection.
 17. The integrated propulsion system for a hybrid electricvehicle of claim 16, wherein said low electrical-resistance connectionis formed by welding, brazing, or soldering.
 18. The hybrid electricvehicle incorporating an integrated propulsion system of claim 12, wheresaid negative electrodes are sintered negative electrodes formed fromOvonic alloys.
 19. The hybrid electric vehicle incorporating anintegrated propulsion system of claim 12, where said negative electrodesare formed from an Ovonic alloy comprising the following composition:(Base Alloy)_(a)Co_(b)Mn_(c)Al_(d)Fe_(e)La_(f)Mo_(g) where Base Alloyrepresents a disordered multicomponent alloy having at least onestructure selected from the group consisting of amorphous,microcrystalline, polycrystalline, and any combination of thesestructures; b is 0 to 7.5 atomic percent; c is 0 to 8.5 atomic percent;d is 0 to 2.5 atomic percent; e is 0 to 6 atomic percent; f is 0 to 4.5atomic percent; g is 0 to 6.5 atomic percent; b+c+d+e+f+g>0; anda+b+c+d+e+f+g=100 atomic percent.
 20. The hybrid electric vehicleincorporating an integrated propulsion system of claim 12, where saidpositive electrodes are formed from disordered γ-phase positiveelectrode material.
 21. The hybrid electric vehicle incorporating anintegrated propulsion system of claim 12, where said porous metalsubstrate is fabricated with current collection lines having electricalconductivity greater than said porous metal substrate, said currentcollection lines providing high conductivity pathways from points remotefrom said at least one electrode tab on said negative and positiveelectrodes.
 22. The hybrid electric vehicle incorporating an integratedpropulsion system of claim 21, where all connections between said porousmetal substrate, said current collection lines, and said at least oneelectrode tab are laser welded.
 23. The hybrid electric vehicleincorporating an integrated propulsion system of claim 12 where saidpositive electrodes further comprise current conducting additives addedto said powdered active material of said positive electrodes, saidcurrent conducting additives chosen from the group consisting of nickelparticles, nickel fibers, graphite particles, nickel plated graphiteparticles, nickel plated copper particles, nickel plated copper fibers,nickel flakes, and nickel plated copper flakes.
 24. The hybrid electricvehicle incorporating an integrated propulsion system of claim 10,wherein said nickel metal hydride batteries are low pressure nickelmetal hydride electrochemical cells comprising: a negative electrode ofmetal hydride; a positive electrode of nickel hydroxide; and a reducedthickness separator of nylon or grafted polyethylene positioned aroundsaid negative electrode and around said positive electrode.
 25. Thehybrid electric vehicle incorporating an integrated propulsion system ofclaim 25, where said negative electrode or the surface of said reducedthickness separator facing said negative electrode has a uniformdistribution of hydrophobic material to increase gas recombination andreduce cell pressure.
 26. The hybrid electric vehicle incorporating anintegrated propulsion system of claim 26, where said hydrophobicmaterial comprises a 1% aqueous solution of polytetrafluoroethylene. 27.The hybrid electric vehicle incorporating an integrated propulsionsystem of claim 10, wherein the battery pack comprises a fluid cooledbattery-pack system, said system including: a battery-pack case, saidcase including at least one coolant inlet means and at least one coolantoutlet means; at least one battery module disposed within said case,said battery module including a plurality of individual batteriesbundled together, said at least one battery module being positionedwithin said case such that said battery module is spacedly disposed fromsaid case and from any other battery modules disposed within said caseto form coolant flow channels along at least one surface of said bundledbatteries, the width of said coolant flow channels optimally sized toallow for maximum heat transfer, through convective, conductive andradiative heat transfer mechanisms, from said batteries to said coolant;and at least one coolant transport means, said coolant transport meanscausing said coolant to enter said coolant inlet means of said case, toflow through said coolant flow channels and to exit said coolant outletmeans of said case.
 28. The hybrid electric vehicle incorporating anintegrated propulsion system of claim 27, where said coolant transportmeans includes a forced-air blower.
 29. The hybrid electric vehicleincorporating an integrated propulsion system of claim 27, where saidcoolant flows perpendicular to the longest dimension of said coolantflow channels.
 30. The hybrid electric vehicle incorporating anintegrated propulsion system of claim 27, where said coolant flowsparallel to the longest dimension of said coolant flow channels.
 31. Thehybrid electric vehicle incorporating an integrated propulsion system ofclaim 27, where said coolant flow channels are designed to impede theflow of coolant flowing therethrough by no more than about 5 to 30% inflow volume.
 32. The hybrid electric vehicle incorporating an integratedpropulsion system of claim 27, where the width of said coolant flowchannels is between 0.3 and 12 mm.
 33. The hybrid electric vehicleincorporating an integrated propulsion system of claim 27, where saidsystem maintains the temperature of said battery modules below 65° C.34. The hybrid electric vehicle incorporating an integrated propulsionsystem of claim 27, where said system maintains the temperaturedifference between battery modules below 8° C.